8=4.9t^2+30t

Solution for 8=4.9t^2+30t equation:

8=4.9t^2+30t

We move all terms to the left:

8-(4.9t^2+30t)=0

We get rid of parentheses

-4.9t^2-30t+8=0

a = -4.9; b = -30; c = +8;
Δ = b2-4ac
Δ = -302-4·(-4.9)·8
Δ = 1056.8
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-30)-\sqrt{1056.8}}{2*-4.9}=\frac{30-\sqrt{1056.8}}{-9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-30)+\sqrt{1056.8}}{2*-4.9}=\frac{30+\sqrt{1056.8}}{-9.8}
$